Secondary battery and method of manufacturing the same

ABSTRACT

A negative-electrode terminal that is secured to a sealing plate is connected to a first negative-electrode current collector. A negative-electrode tab that is connected to the negative-electrode sheet is connected to a second negative-electrode current collector. The first negative-electrode current collector and the second negative-electrode current collector are disposed along the sealing plate. The second negative-electrode current collector has an opening. The second negative-electrode current collector is disposed on the first negative-electrode current collector such that the opening faces the first negative-electrode current collector. The second negative-electrode current collector is welded to the first negative-electrode current collector around the opening.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention application claims priority to Japanese PatentApplication No. 2018-005266 filed in the Japan Patent Office on Jan. 17,2018, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a secondary battery and a method ofmanufacturing the secondary battery.

Description of Related Art

Prismatic secondary batteries such as alkali secondary batteries andnon-aqueous electrolyte secondary batteries are used in power sourcesfor driving, for example, electric vehicles (EVs) and hybrid electricvehicles (HEVs or PHEVs).

Each of the prismatic secondary batteries includes a battery case formedof a prismatic exterior body in the form of a tube having an opening anda bottom and a sealing plate that seals the opening of the exteriorbody. In the battery case, an electrode body and an electrolyte solutionare accommodated, and the electrode body is formed of apositive-electrode sheet, a negative-electrode sheet, and a separator. Apositive-electrode terminal and a negative-electrode terminal aresecured to the sealing plate. The positive-electrode terminal iselectrically connected to the positive-electrode sheet with apositive-electrode current collector interposed therebetween. Thenegative-electrode terminal is electrically connected to thenegative-electrode sheet with a negative-electrode current collectorinterposed therebetween.

In some prismatic secondary batteries, a terminal and a tab of anelectrode sheet are connected by a current collector member formed ofplural components (see Japanese Published Unexamined Patent ApplicationNo. 2005-142026 (Patent Document 1)).

The current collector member that is formed of plural componentsfacilitates manufacture of a secondary battery having an increasedvolume energy density unlike the case where the current collector memberis a single component.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a secondary batteryin which a current collector member that electrically connects aterminal and a tab of an electrode sheet to each other is formed of afirst current collector and a second current collector and thereliability of a joint between the first current collector and thesecond current collector is high, and a method of manufacturing thesecondary battery.

A secondary battery according to an embodiment of the present inventionincludes an electrode body that includes a positive-electrode sheet anda negative-electrode sheet, an exterior body that has an opening andthat accommodates the electrode body, a sealing plate that seals theopening, a terminal that is secured to the sealing plate, a tab that isconnected to the positive-electrode sheet or the negative-electrodesheet, and a first current collector and a second current collector thatelectrically connect the terminal and the tab to each other. The firstcurrent collector is connected to the terminal. The second currentcollector is connected to the tab. The second current collector has anopening. The second current collector is disposed on the first currentcollector and welded to the first current collector around the opening.

With the structure of the secondary battery according to the embodimentof the present invention, the secondary battery has high reliability ofa joint between the first current collector and the second currentcollector. In addition, the secondary battery readily has an increasedvolume energy density. The first current collector and the secondcurrent collector are preferably disposed along the sealing plate. Thefirst current collector may be a first positive-electrode currentcollector or a first negative-electrode current collector, and thesecond current collector may be a second positive-electrode currentcollector or a second negative-electrode current collector.

A positive-electrode tab that is connected to the positive-electrodesheet and a negative-electrode tab that is connected to thenegative-electrode sheet are preferably disposed on an end portion ofthe electrode body facing the sealing plate. A joint between thepositive-electrode tab and the second positive-electrode currentcollector is preferably disposed nearer to the sealing plate than aportion of a positive electrode active material mixture layer that isnearest to the sealing plate in the thickness direction of the sealingplate. A joint between the negative-electrode tab and the secondnegative-electrode current collector is preferably disposed nearer tothe sealing plate than a portion of a negative electrode active materialmixture layer that is nearest to the sealing plate in the thicknessdirection of the sealing plate. In this case, the secondary battery hasan increased volume energy density. A plurality of thepositive-electrode tabs are more preferably stacked, and thepositive-electrode tabs that are stacked are more preferably bent. Aplurality of the negative-electrode tabs are more preferably stacked,and the negative-electrode tabs that are stacked are more preferablybent.

The tab is preferably connected to a surface of the second currentcollector facing the electrode body.

The second current collector preferably includes a thin portion, and thethin portion preferably has the opening. A portion of the second currentcollector that is located away from the opening is preferably welded tothe first current collector.

An insulating member is preferably disposed between the sealing plateand the first current collector. A portion of the insulating member thatfaces a back surface of a portion of the first current collector that iswelded to the second current collector preferably has a recessedportion.

The second current collector preferably includes a tab joint that isconnected to the tab and a current-collector joint that is connected tothe first current collector. A distance between the sealing plate andthe tab joint in a thickness direction of the sealing plate ispreferably shorter than a distance between the sealing plate and thecurrent-collector joint.

A portion of the first current collector that faces the openingpreferably has a flat surface.

The first current collector preferably includes a projection that has anasymmetric shape in a plan view in a region in which the first currentcollector does not face the second current collector.

The electrode body preferably includes a first tab group that includes aplurality of the tabs and a second tab group that includes a pluralityof the tabs. The first tab group and the second tab group preferablybend in different directions. The first tab group and the second tabgroup are preferably connected to a surface of the second currentcollector facing the electrode body.

A method of manufacturing a secondary battery according to an embodimentof the present invention is a method of manufacturing a secondarybattery including an electrode body that includes a positive-electrodesheet and a negative-electrode sheet, an exterior body that has anopening and that accommodates the electrode body, a sealing plate thatseals the opening, a terminal that is secured to the sealing plate, atab that is connected to the positive-electrode sheet or thenegative-electrode sheet, and a first current collector and a secondcurrent collector that electrically connect the terminal and the tab toeach other. The first current collector is connected to the terminal.The second current collector is connected to the tab. The methodincludes a terminal connecting step of connecting the terminal to thefirst current collector, a tab connecting step of connecting the tab tothe second current collector, a step of disposing the second currentcollector that has an opening on the first current collector such thatthe opening faces the first current collector after the terminalconnecting step and the tab connecting step, and a current collectorconnecting step of checking presence or absence of a gap between thefirst current collector and the second current collector, or the size ofthe gap, or both through the opening after the step of disposing thesecond current collector and subsequently welding the first currentcollector and the second current collector to each other by radiatingenergy rays.

With the method of manufacturing the secondary battery according to theembodiment of the present invention, the secondary battery has highreliability of the joint between the first current collector and thesecond current collector. In addition, the secondary battery readily hasan increased volume energy density. The terminal connecting step and thetab connecting step may be performed in either order. The first currentcollector and the second current collector are preferably disposed alongthe sealing plate.

The method preferably further includes a step of disposing the firstcurrent collector on the sealing plate with an insulating memberinterposed therebetween before the terminal connecting step. The step ofdisposing the second current collector preferably includes disposing thesecond current collector on the sealing plate with the insulating memberinterposed therebetween.

The current collector connecting step preferably includes radiating theenergy rays toward a position away from the opening to weld the firstcurrent collector and the second current collector to each other at theposition away from the opening.

According to the present invention, a secondary battery having highreliability can be provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view of a secondary battery according to anembodiment.

FIG. 2 is a sectional view of FIG. 1 taken along line II-II.

FIG. 3 is a plan view of a positive-electrode sheet according to theembodiment.

FIG. 4 is a plan view of a negative-electrode sheet according to theembodiment.

FIG. 5 is a plan view of an electrode element according to theembodiment.

FIG. 6 illustrates positive-electrode tab groups that are connected to apositive-electrode current collector and negative-electrode tab groupsthat are connected to a negative-electrode current collector.

FIG. 7 illustrates a surface of a sealing plate facing an electrode bodyafter a first positive-electrode current collector and a firstnegative-electrode current collector are secured.

FIG. 8A is a sectional view of the vicinity of a positive-electrodeterminal taken along the transverse direction of the sealing platebefore the positive-electrode terminal is crimped.

FIG. 8B is a sectional view of the vicinity of the positive-electrodeterminal taken along the transverse direction of the sealing plate afterthe positive-electrode terminal is crimped.

FIG. 8C is a sectional view of the vicinity of the positive-electrodeterminal taken along the transverse direction of the sealing plate afterthe positive-electrode terminal and the first positive-electrode currentcollector are welded.

FIG. 9A is an enlarged view of the positive-electrode terminal near acrimped portion thereof in FIG. 8B.

FIG. 9B is an enlarged view of the positive-electrode terminal near thecrimped portion in FIG. 8C.

FIG. 10 illustrates the surface of the sealing plate facing theelectrode body after a second positive-electrode current collector issecured to the first positive-electrode current collector and a secondnegative-electrode current collector is secured to the firstnegative-electrode current collector.

FIG. 11 is a sectional view of the vicinity of a negative-electrodeterminal taken along the longitudinal direction of the sealing plate.

FIG. 12 is an enlarged view of the vicinity of a joint between the firstnegative-electrode current collector and the second negative-electrodecurrent collector in FIG. 11.

FIG. 13A and FIG. 13B illustrate perspective views of the sealing plateand a cover after components are secured.

FIG. 14 is a sectional view of the vicinity of the positive-electrodeterminal taken along the transverse direction of the sealing plate.

FIG. 15 is a sectional view of the vicinity of the positive-electrodeterminal taken along the longitudinal direction of the sealing plate.

DETAILED DESCRIPTION OF THE INVENTION

The structure of a prismatic secondary battery 20 that corresponds to asecondary battery according to an embodiment will hereinafter bedescribed. The present invention is not limited to the embodimentdescribed below.

As illustrated in FIG. 1 and FIG. 2, the prismatic secondary battery 20includes a battery case 100 formed of a prismatic exterior body 1 in theform of a prism having an opening and a bottom and a sealing plate 2that seals the opening of the prismatic exterior body 1. The prismaticexterior body 1 and the sealing plate 2 are preferably composed of ametal and are preferably composed of, for example, aluminum or aluminumalloy. In the prismatic exterior body 1, an electrode body 3 and anelectrolyte are accommodated, and the electrode body 3 is formed ofpositive-electrode sheets and negative-electrode sheets that are stackedwith separators interposed therebetween.

Positive-electrode tabs 40 and negative-electrode tabs 50 are disposedon an end portion of the electrode body 3 facing the sealing plate 2.The positive-electrode tabs 40 are electrically connected to apositive-electrode terminal 7 with a second positive-electrode currentcollector 6 b and a first positive-electrode current collector 6 ainterposed therebetween. The negative-electrode tabs 50 are electricallyconnected to a negative-electrode terminal 9 with a secondnegative-electrode current collector 8 b and a first negative-electrodecurrent collector 8 a interposed therebetween.

The first positive-electrode current collector 6 a, the secondpositive-electrode current collector 6 b, and the positive-electrodeterminal 7 are preferably composed of a metal and more preferablycomposed of aluminum or aluminum alloy. An outer insulating member 10composed of a resin is disposed between the positive-electrode terminal7 and the sealing plate 2. An inner insulating member 11 composed of aresin is disposed between the first positive-electrode current collector6 a and the and the sealing plate 2 and between the secondpositive-electrode current collector 6 b and the sealing plate 2.

The first negative-electrode current collector 8 a, the secondnegative-electrode current collector 8 b, and the negative-electrodeterminal 9 are preferably composed of a metal and more preferablycomposed of copper or copper alloy. The negative-electrode terminal 9preferably includes a portion composed of aluminum or aluminum alloy anda portion composed of copper or copper alloy. In this case, the portioncomposed of copper or copper alloy is preferably connected to the firstnegative-electrode current collector 8 a, and the portion composed ofaluminum or aluminum alloy preferably projects toward the outside beyondthe sealing plate 2. An outer insulating member 12 composed of a resinis disposed between the negative-electrode terminal 9 and the sealingplate 2. An inner insulating member 13 composed of a resin is disposedbetween the first negative-electrode current collector 8 a and thesealing plate 2 and between the second negative-electrode currentcollector 8 b and the sealing plate 2.

An electrode body holder 14 that is formed of a resin sheet is disposedbetween the electrode body 3 and the prismatic exterior body 1. Theelectrode body holder 14 is preferably molded by bending an insulatingsheet composed of a resin into a bag shape or a box shape. The sealingplate 2 has an electrolytic solution injection hole 15. The electrolyticsolution injection hole 15 is sealed by a sealing member 16. A gasexhausting valve 17 is disposed in the sealing plate 2. The gasexhausting valve 17 is broken when the pressure in the battery case 100becomes a certain pressure or more, and gas in the battery case 100 isdischarged therefrom to the outside of the battery case 100. An annularprojection 2 c is formed on the surface of the sealing plate 2 on theinner side of the battery around the gas exhausting valve 17.

A method of manufacturing the prismatic secondary battery 20 and thestructure thereof will now be described in detail.

Positive-Electrode Sheet

FIG. 3 is a plan view of a positive-electrode sheet 4. Thepositive-electrode sheet 4 includes a main body in which positiveelectrode active material mixture layers 4 b including a positiveelectrode active material are formed on both surfaces of a rectangularpositive-electrode core 4 a. The positive-electrode core 4 a projectsfrom an end side of the main body. The positive-electrode core 4 a thatprojects forms the positive-electrode tabs 40. The positive-electrodetabs 40 may be parts of the positive-electrode core 4 a as illustratedin FIG. 3. Other members that are connected to the positive-electrodecore 4 a may be used as the positive-electrode tabs 40. Apositive-electrode protection layer 4 d having an electric resistancelarger than the electric resistance of the positive electrode activematerial mixture layers 4 b are preferably disposed on a portion of thepositive-electrode tab 40 adjacent to the positive electrode activematerial mixture layers 4 b. A metal foil such as an aluminum foil oraluminum alloy foil is preferably used as the positive-electrode core 4a. For example, a lithium transition metal composite oxide is preferablyused as the positive electrode active material.

Negative-Electrode Sheet

FIG. 4 is a plan view of a negative-electrode sheet 5. Thenegative-electrode sheet 5 includes a main body in which negativeelectrode active material mixture layers 5 b including a negativeelectrode active material are formed on both surfaces of a rectangularnegative-electrode core 5 a. The negative-electrode core 5 a projectsfrom an end side of the main body. The negative-electrode core 5 a thatprojects forms the negative-electrode tabs 50. The negative-electrodetabs 50 may be parts of the negative-electrode core 5 a as illustratedin FIG. 4. Other members that are connected to the negative-electrodecore 5 a may be used as the negative-electrode tabs 50. A metal foilsuch as a copper foil or copper alloy foil is preferably used as thenegative-electrode core 5 a. For example, a carbon material or a siliconmaterial is preferably used as the negative electrode active material.

Manufacture of Electrode Body Element

The above method is used to manufacture 50 positive-electrode sheets 4and 51 negative-electrode sheets 5. These are stacked with polyolefinrectangular separators interposed therebetween to manufacture multilayerelectrode body elements (a first electrode body element 3 a and a secondelectrode body element 3 b). As illustrated in FIG. 5, the multilayerelectrode body elements (the first electrode body element 3 a and thesecond electrode body element 3 b) include positive-electrode tab groups(a first positive-electrode tab group 40 a and a secondpositive-electrode tab group 40 b) and negative-electrode tab groups (afirst negative-electrode tab group 50 a and a second negative-electrodetab group 50 b). The positive-electrode tabs 40 of thepositive-electrode sheets 4 are stacked on end portions of thepositive-electrode tab groups. The negative-electrode tabs 50 of thenegative-electrode sheets 5 are stacked on end portions of thenegative-electrode tab groups.

Some of the separators are located on both outer surfaces of eachelectrode body element. The electrode sheets and the separators that arestacked can be secured with, for example, a tape. Alternatively,adhesive layers may be formed on each separator, the separator and thecorresponding positive-electrode sheet 4 may adhere to each other, andthe separator and the corresponding negative-electrode sheet 5 mayadhere to each other. The separators may be formed in a jig zag patternto stack the positive-electrode sheets 4 and the negative-electrodesheets 5.

The size of each separator in a plan view is preferably equal to orlarger than the size of each negative-electrode sheet 5. Eachpositive-electrode sheet 4 or each negative-electrode sheet 5 may bedisposed between two separators, and the positive-electrode sheets 4 andthe negative-electrode sheets 5 may be stacked after the peripheries ofthe separators are thermally welded to each other. A belt-likepositive-electrode sheet and a belt-like negative-electrode sheet may bewound with a belt-like separator interposed therebetween to form a woundelectrode body element.

Connection Between Current Collector and Tab

The two electrode body elements, which are the first electrode bodyelement 3 a and the second electrode body element 3 b, are manufacturedin the above manner. The first electrode body element 3 a and the secondelectrode body element 3 b may have the same structure or may havedifferent structures. The positive-electrode tabs 40 of the firstelectrode body element 3 a form the first positive-electrode tab group40 a. The negative-electrode tabs 50 of the first electrode body element3 a form the first negative-electrode tab group 50 a. Thepositive-electrode tabs 40 of the second electrode body element 3 b formthe second positive-electrode tab group 40 b. The negative-electrodetabs 50 of the second electrode body element 3 b form the secondnegative-electrode tab group 50 b.

FIG. 6 illustrates the first positive-electrode tab group 40 a and thesecond positive-electrode tab group 40 b that are connected to thesecond positive-electrode current collector 6 b and the firstnegative-electrode tab group 50 a and the second negative-electrode tabgroup 50 b that are connected to the second negative-electrode currentcollector 8 b. The second positive-electrode current collector 6 b andthe second negative-electrode current collector 8 b are disposed betweenthe first electrode body element 3 a and the second electrode bodyelement 3 b. The first positive-electrode tab group 40 a and the secondpositive-electrode tab group 40 b are disposed on the secondpositive-electrode current collector 6 b. The first negative-electrodetab group 50 a and the second negative-electrode tab group 50 b aredisposed on the second negative-electrode current collector 8 b. Thefirst positive-electrode tab group 40 a and the secondpositive-electrode tab group 40 b are welded to the secondpositive-electrode current collector 6 b to form welds 60. The firstnegative-electrode tab group 50 a and the second negative-electrode tabgroup 50 b are welded to the second negative-electrode current collector8 b to form welds 61. A welding method is preferably ultrasonic weldingor resistance welding. The laser welding can be used for connection. Inthe positive-electrode current collectors 6, a current collector opening6 e is formed at a position at which the positive-electrode currentcollector faces the electrolytic solution injection hole 15.

The second positive-electrode current collector 6 b has an opening 6 c.The opening 6 c is formed within a thin portion 6 d. The secondnegative-electrode current collector 8 b has an opening 8 c. The opening8 c is formed within a thin portion 8 d.

Securing Components to Sealing Plate

The outer insulating member 10 is disposed on the sealing plate 2 on theouter surface side of the battery around a positive-electrode terminalinsertion hole 2 a. The inner insulating member 11 and the firstpositive-electrode current collector 6 a are disposed on the sealingplate 2 on the inner surface side of the battery around thepositive-electrode terminal insertion hole 2 a. The positive-electrodeterminal 7 is inserted into a through-hole of the outer insulatingmember 10, the positive-electrode terminal insertion hole 2 a of thesealing plate 2, a through-hole of the inner insulating member 11, and aterminal connection hole of the first positive-electrode currentcollector 6 a from the outside of the battery. An end portion of thepositive-electrode terminal 7 is crimped on the first positive-electrodecurrent collector 6 a. Consequently, the positive-electrode terminal 7and the first positive-electrode current collector 6 a are secured tothe sealing plate 2. A crimped portion of the positive-electrodeterminal 7 and the first positive-electrode current collector 6 a arepreferably welded to each other.

The outer insulating member 12 is disposed on the sealing plate 2 on theouter surface side of the battery around a negative-electrode terminalinsertion hole 2 b. The inner insulating member 13 and the firstnegative-electrode current collector 8 a are disposed on the sealingplate 2 on the inner surface side of the battery around thenegative-electrode terminal insertion hole 2 b. The negative-electrodeterminal 9 is inserted into a through-hole of the outer insulatingmember 12, the negative-electrode terminal insertion hole 2 b of thesealing plate 2, a through-hole of the inner insulating member 13, and aterminal connection hole of the first negative-electrode currentcollector 8 a from the outside of the battery. An end portion of thenegative-electrode terminal 9 is crimped on the first negative-electrodecurrent collector 8 a. Consequently, the negative-electrode terminal 9and the first negative-electrode current collector 8 a are secured tothe sealing plate 2. A crimped portion of the negative-electrodeterminal 9 and the first negative-electrode current collector 8 a arepreferably welded to each other.

FIG. 7 illustrates the surface of the sealing plate 2 on the innersurface side of the battery after the positive-electrode terminal 7, theouter insulating member 10, the inner insulating member 11, the firstpositive-electrode current collector 6 a, the negative-electrodeterminal 9, the outer insulating member 12, the inner insulating member13, and the first negative-electrode current collector 8 a are secured.The inner insulating member 11 on the positive electrode side includes abase 11 a that is disposed along the sealing plate 2. A pair of secondwalls 11 b that project from the base 11 a toward the electrode body 3are disposed on both ends of the base 11 a in the transverse directionof the sealing plate 2. A pair of first walls 11 c that project from thebase 11 a toward the electrode body 3 are disposed on both ends of thebase 11 a in the transverse direction of the sealing plate 2. An outercircumferential rib 11 d is disposed along an outer circumference of thebase 11 a of the inner insulating member 11 at a position at which thesecond walls 11 b and the first walls 11 c are not disposed. Asillustrated in FIG. 7, the first positive-electrode current collector 6a and the positive-electrode terminal 7 are connected to each otherbetween the pair of the first walls 11 c.

A current-collector projection 6 x is formed on the surface of the firstpositive-electrode current collector 6 a facing the electrode body 3.The shape of the current-collector projection 6 x in a plan view ispreferably a shape having the longitudinal direction and the transversedirection such as a rectangle, an ellipse, or a track shape.

The inner insulating member 13 on the negative electrode side includes abase 13 a that is disposed along the sealing plate 2. A pair of thirdwalls 13 b that project from the base 13 a toward the electrode body 3are disposed on both ends of the base 13 a in the transverse directionof the sealing plate 2. An outer circumferential rib 13 c is disposedalong an outer circumference of the base 13 a of the inner insulatingmember 13 at a position at which the third walls 13 b are not disposed.

A current-collector projection 8 x is formed on the surface of the firstnegative-electrode current collector 8 a facing the electrode body 3.The shape of the current-collector projection 8 x in a plan view ispreferably a shape having the longitudinal direction and the transversedirection such as a rectangle, an ellipse, or a track shape.

Connection Between Terminal and Current Collector

A method of connecting the negative-electrode terminal 9 and the firstnegative-electrode current collector 8 a to each other is taken as anexample to describe a method of connecting the positive-electrodeterminal 7 and the first positive-electrode current collector 6 a toeach other and a method of connecting the negative-electrode terminal 9and the first negative-electrode current collector 8 a to each other.The positive-electrode terminal 7 and the first positive-electrodecurrent collector 6 a can be connected to each other in the same manneras the negative-electrode terminal 9 and the first negative-electrodecurrent collector 8 a are connected to each other.

As illustrated in FIG. 8A, an insertion portion 9 b that is disposed ona flange 9 a of the negative-electrode terminal 9 is inserted into aterminal connection hole 8 y that is formed in the firstnegative-electrode current collector 8 a. A tapered portion 8 z isformed around the terminal connection hole 8 y and has an inner diameterthat gradually increases toward the end portion thereof farther from thesealing plate 2. The insertion portion 9 b is inserted into the terminalconnection hole 8 y from the sealing plate 2. The negative-electrodeterminal 9 preferably includes a first metal portion 9 x composed of afirst metal and a second metal portion 9 y composed of a second metalthat differs from the first metal. The first metal is preferablyaluminum or aluminum alloy. The second metal is preferably copper orcopper alloy. A layer composed of a third metal may be formed betweenthe first metal portion 9 x and the second metal portion 9 y. The thirdmetal is preferably nickel, or another metal.

Subsequently, as illustrated in FIG. 8B, an end of the insertion portion9 b of the negative-electrode terminal 9 is deformed such that thediameter of the end is increased to form a crimped portion 9 c.Consequently, a region of the insertion portion 9 b on the end side iscrimped on the first negative-electrode current collector 8 a. Thecrimped portion 9 c is crimped on the tapered portion 8 z. A gap 95 isformed between the tapered portion 8 z and the insertion portion 9 b.The crimped portion 9 c has an outer diameter larger than the minimuminner diameter thereof around the terminal connection hole 8 y. A partof the crimped portion 9 c projects away from the sealing plate 2 beyonda surface 8 a 1 of the first negative-electrode current collector 8 afarther from the sealing plate 2. A recessed end portion 9 d ispreferably formed on an end surface of the insertion portion 9 b. Therecessed end portion 9 d that is formed on the end surface of theinsertion portion 9 b enables the crimped portion 9 c to be more stablyformed. Energy rays such as laser rays are radiated toward the gap 95 tomelt the crimped portion 9 c and the tapered portion 8 z of the firstnegative-electrode current collector 8 a. The melted portions aresolidified, and, as illustrated in FIG. 8C, a solidified portion 70 isformed. The negative-electrode terminal 9 and the firstnegative-electrode current collector 8 a are joined to each other withthe solidified portion 70. The metal of which the negative-electrodeterminal 9 or the first negative-electrode current collector 8 a that ismelted is composed flows into the gap 95 and solidifies. The solidifiedportion 70 has a recessed portion 70 a.

In the case where the negative-electrode terminal 9 and the firstnegative-electrode current collector 8 a are connected to each other inthe above manner, the negative-electrode terminal 9 and the firstnegative-electrode current collector 8 a are more firmly connected toeach other, and the prismatic secondary battery 20 has high reliability.In the case where the melted metal flows into the gap 95 between thecrimped portion 9 c of the negative-electrode terminal 9 and the taperedportion 8 z of the first negative-electrode current collector 8 a suchthat the solidified portion 70 that is solidified from the melted metalhas the recessed portion 70 a, overlap, which is a welding defect, canbe inhibited from occurring. In addition, the solidified portion 70 canbe effectively inhibited from having a bulge shape. Accordingly, thesolidified portion 70 is unlikely to be damaged, and the reliability ofthe prismatic secondary battery 20 increases.

The bottom of the recessed portion 70 a is located nearer to the sealingplate 2 (lower side in FIG. 9B) than the surface 8 a 1 (the uppersurface of the first negative-electrode current collector 8 a in FIG.9B) of the first negative-electrode current collector 8 a farther fromthe sealing plate 2. This makes overlap, which is a welding defect,unlikely to occur during welding. Accordingly, a part of the solidifiedportion 70 can be effectively prevented from chipping and falling, and ashort circuit is effectively prevented from occurring. In addition, thesolidified portion 70 is more unlikely to be damaged.

The negative-electrode terminal 9 is preferably crimped such that thecrimped portion 9 c of the negative-electrode terminal 9 projects awayfrom the sealing plate 2 (upward in FIG. 8B) beyond the surface 8 a 1 ofthe first negative-electrode current collector 8 a farther from thesealing plate 2. The amount of the melt (the volume of the meltedportion) of the negative-electrode terminal 9 due to the energy rays ispreferably larger than the amount of the melt (the volume of the meltedportion) of the first negative-electrode current collector 8 a due tothe energy rays. This enables the melted metal to readily enter the gap95, and the negative-electrode terminal 9 and the firstnegative-electrode current collector 8 a are more firmly connected toeach other.

A bottom and side walls that define the recessed portion 70 a correspondto the solidified portion 70 that is solidified from the melted metaldue to the energy rays. The thickness of a portion 70 x of thesolidified portion 70 that is located at the bottom of the recessedportion 70 a in the thickness direction (vertical direction in FIG. 9B)of the first negative-electrode current collector 8 a is preferably morethan the thickness of a portion 70 y of the solidified portion 70 thatis located at one of the side walls of the recessed portion 70 a in theradial direction (left-right direction in FIG. 9B) of the terminalconnection hole 8 y. With this structure, the negative-electrodeterminal 9 and the first negative-electrode current collector 8 a areconnected in a more preferable state. In addition, the solidifiedportion 70 is more unlikely to be damaged.

It is preferable that a portion of the negative-electrode terminal 9that is farthest from the sealing plate 2 in the thickness direction ofthe sealing plate 2 be not melted due to the energy rays. In this case,a manufacturing apparatus, a jig, and other components are unlikely tocome into contact with the solidified portion 70.

The energy rays may be continuously radiated or may be radiated in apulsed manner. The recessed portion 70 a is preferably annular whenviewed from the thickness direction (direction vertical to the sealingplate 2) of the sealing plate 2.

Connection Between First Current Collector and Second Current Collector

FIG. 10 illustrates the surface of the sealing plate 2 facing theelectrode body 3 after the second positive-electrode current collector 6b is secured to the first positive-electrode current collector 6 a andthe second negative-electrode current collector 8 b is secured to thefirst negative-electrode current collector 8 a. The secondpositive-electrode current collector 6 b that is connected to the firstpositive-electrode tab group 40 a and the second positive-electrode tabgroup 40 b is disposed on the base 11 a of the inner insulating member11. A part of the second positive-electrode current collector 6 b isdisposed on the first positive-electrode current collector 6 a. The thinportion 6 d of the second positive-electrode current collector 6 b iswelded to the first positive-electrode current collector 6 a, and a weld62 is formed. The weld 62 is formed so as to be away from the opening 6c. The weld 62 is preferably formed by energy rays such as laser rays.

The second negative-electrode current collector 8 b that is connected tothe first negative-electrode tab group 50 a and the secondnegative-electrode tab group 50 b is disposed on the base 13 a of theinner insulating member 13. A part of the second negative-electrodecurrent collector 8 b is disposed on the first negative-electrodecurrent collector 8 a. The thin portion 8 d of the secondnegative-electrode current collector 8 b is welded to the firstnegative-electrode current collector 8 a, and a weld 63 is formed. Theweld 63 is formed so as to be away from the opening 8 c. The weld 63 ispreferably formed by energy rays such as laser rays.

A method of connecting the first negative-electrode current collector 8a and the second negative-electrode current collector 8 b to each otheris taken as an example to describe a method of connecting the firstpositive-electrode current collector 6 a and the secondpositive-electrode current collector 6 b to each other and a method ofconnecting the first negative-electrode current collector 8 a and thesecond negative-electrode current collector 8 b to each other.

FIG. 11 is a sectional view of the vicinity of the negative-electrodeterminal 9 taken along the longitudinal direction of the sealing plate2. The second negative-electrode current collector 8 b includes a tabjoint 8 b 1 that is connected to the negative-electrode tabs 50 (thefirst negative-electrode tab group 50 a and the secondnegative-electrode tab group 50 b) and a current-collector joint 8 b 2that is connected to the first negative-electrode current collector 8 a.A step portion 8 b 3 is disposed between the tab joint 8 b 1 and thecurrent-collector joint 8 b 2. The tab joint 8 b 1 is disposed on thebase 13 a of the inner insulating member 13. The current-collector joint8 b 2 is disposed on the first negative-electrode current collector 8 a.The thin portion 8 d of the current-collector joint 8 b 2 is welded tothe first negative-electrode current collector 8 a. When the firstnegative-electrode current collector 8 a and the secondnegative-electrode current collector 8 b are welded to each other, theopening 8 c is used to check whether there is no gap between the firstnegative-electrode current collector 8 a and the thin portion 8 d of thesecond negative-electrode current collector 8 b. Alternatively, theopening 8 c is used to check whether the size of a gap between the firstnegative-electrode current collector 8 a and the thin portion 8 d of thesecond negative-electrode current collector 8 b is equal to or less thana predetermined size. This enables the first negative-electrode currentcollector 8 a and the second negative-electrode current collector 8 b tobe stably welded to each other. The presence or absence of the gap orthe size of the gap is preferably checked by using reflection of light.

The energy rays are preferably radiated toward a position away from theopening 8 c to form the weld 63 at the position away from the opening 8c. The weld 63 can be stably formed so as to be firmer than in the casewhere the weld 63 is formed along an edge of the opening 8 c.

An insulating member recessed portion 13 x is formed on the base 13 a ofthe inner insulating member 13. The insulating member recessed portion13 x faces the back surface of the first negative-electrode currentcollector 8 a opposite the surface to which the secondnegative-electrode current collector 8 b is welded. This inhibits theinner insulating member 13 from being damaged due to heat that isgenerated when the first negative-electrode current collector 8 a andthe second negative-electrode current collector 8 b are welded to eachother.

The current-collector projection 8 x is formed on a portion of the firstnegative-electrode current collector 8 a that is not covered by thesecond negative-electrode current collector 8 b. This prevents the firstnegative-electrode current collector 8 a from being oriented in anincorrect direction with certainty when the first negative-electrodecurrent collector 8 a is connected to the negative-electrode terminal 9and secured to the sealing plate 2. The shape of the current-collectorprojection 8 x in a plan view is preferably asymmetric. The shape of thecurrent-collector projection 8 x in a plan view is preferably a shapehaving the longitudinal direction and the transverse direction. Aplurality of the current-collector projections 8 x may be formed. Forexample, the current-collector projections 8 x each of which has aperfect circle shape or a square shape in a plan view may be formed. Apart of the second negative-electrode current collector 8 b is disposedon a flat surface of the first negative-electrode current collector 8 a.

Cover

FIG. 13A and FIG. 13B illustrate perspective views of the vicinity ofthe positive-electrode terminal 7 after the second positive-electrodecurrent collector 6 b is connected to the first positive-electrodecurrent collector 6 a. In FIG. 13A and FIG. 13B, the firstpositive-electrode tab group 40 a and the second positive-electrode tabgroup 40 b that are connected to the second positive-electrode currentcollector 6 b are not illustrated. FIG. 14 is a sectional view of thevicinity of the positive-electrode terminal 7 taken along the transversedirection of the sealing plate 2 with a cover 80 connected to the innerinsulating member 11.

The cover 80 composed of a resin is connected to the inner insulatingmember 11. The cover 80 is disposed between the first positive-electrodecurrent collector 6 a and the electrode body 3. This prevents theelectrode body 3 from coming into contact with the firstpositive-electrode current collector 6 a and the sealing plate 2although the electrode body 3 moves toward the sealing plate 2 in somecases. In the case where the cover 80 and the inner insulating member 11are separated components, the secondary battery is more readilymanufactured.

The positive-electrode tabs 40 and the positive-electrode terminal 7 canbe connected by the first positive-electrode current collector 6 a andthe second positive-electrode current collector 6 b. In this case, aportion of the cover 80 that is nearest to the electrode body 3 in thethickness direction of the sealing plate 2 is preferably located nearerto the electrode body 3 than a portion of the positive-electrodeterminal 7, a portion of the first positive-electrode current collector6 a, and a portion of the second positive-electrode current collector 6b that are nearest to the electrode body 3.

The positive-electrode tabs 40 and the positive-electrode terminal 7 canbe connected only by the first positive-electrode current collectorwithout using the second positive-electrode current collector. In thiscase, the portion of the cover 80 that is nearest to the electrode body3 in the thickness direction of the sealing plate 2 is preferablylocated nearer to the electrode body 3 than the portion of thepositive-electrode terminal 7 and the portion of the firstpositive-electrode current collector that are nearest to the electrodebody 3.

The cover 80 composed of a resin is connected to the inner insulatingmember 11 after the second positive-electrode current collector 6 b isconnected to the first positive-electrode current collector 6 a. Thecover 80 is preferably connected to the inner insulating member 11 afterthe second positive-electrode current collector 6 b that is connected tothe first positive-electrode tab group 40 a and the secondpositive-electrode tab group 40 b is connected to the firstpositive-electrode current collector 6 a and before the first electrodebody element 3 a and the second electrode body element 3 b areintegrated into one piece.

The cover 80 includes a cover portion 80 a that faces the firstpositive-electrode current collector 6 a. The cover portion 80 a isdisposed between the first positive-electrode current collector 6 a andthe electrode body 3. The cover portion 80 a preferably faces a jointbetween the first positive-electrode current collector 6 a and thesecond positive-electrode current collector 6 b. The cover 80 includes apair of cover joints 80 b that extend from the cover portion 80 a towardthe sealing plate 2. The cover joints 80 b are connected to the innerinsulating member 11. The first walls 11 c of the inner insulatingmember 11 preferably extend toward the electrode body 3 beyond thesurface of the first positive-electrode current collector 6 a facing theelectrode body 3. The cover joints 80 b are preferably connected toportions of the first walls 11 c that are located nearer to theelectrode body 3 than the surface of the first positive-electrodecurrent collector 6 a facing the electrode body 3. The first walls 11 cof the inner insulating member 11 can have connection openings 11 e.Each cover joint 80 b includes a wall 80 b 1 that extends from the coverportion 80 a toward the sealing plate 2 and a connection projection 80 b2 that is disposed on a side surface of the wall 80 b 1. The cover 80can be connected to the inner insulating member 11 in a manner in whichthe connection projections 80 b 2 of the cover joints 80 b are fittedinto the connection openings 11 e of the first walls 11 c. The coverjoints 80 b may have connection openings, and connection projectionsthat are disposed on the first walls 11 c of the inner insulating member11 may be fitted into the connection openings.

The first walls 11 c are preferably disposed on both ends of the innerinsulating member 11 in the transverse direction of the sealing plate 2.The cover joints 80 b are preferably disposed on both ends of the cover80 in the transverse direction of the sealing plate 2. The cover joints80 b and the corresponding first walls 11 c are preferably connected toeach other. Consequently, the inner insulating member 11 and the cover80 are more stably connected to each other.

A gap is preferably formed between the first positive-electrode currentcollector 6 a and the cover portion 80 a in the thickness direction ofthe sealing plate 2. With this structure, the cover portion 80 a candeform so as to bend when the electrode body 3 comes into contact withthe cover portion 80 a, and an impact can be alleviated. The distancebetween the first positive-electrode current collector 6 a and the cover80 in the thickness direction of the sealing plate 2 is preferably 1 mmor more, more preferably 3 mm or more. Root openings 80 c are morepreferably formed in the cover portion 80 a at the roots of the coverjoints 80 b. This enables an impact to be more effectively alleviated.

A gap is preferably formed between the cover portion 80 a and thepositive-electrode terminal 7 in the thickness direction of the sealingplate 2, and it is preferable that the cover portion 80 a and thepositive-electrode terminal 7 be not in contact with each other. Thiseffectively prevents a load from being applied to a joint between thepositive-electrode terminal 7 and the first positive-electrode currentcollector 6 a.

As illustrated in FIG. 15, the second positive-electrode currentcollector 6 b includes a tab joint 6 b 1 that is connected to thepositive-electrode tabs 40 and a current-collector joint 6 b 2 that isconnected to the first positive-electrode current collector 6 a. A stepportion 6 b 3 is formed between the tab joint 6 b 1 and thecurrent-collector joint 6 b 2. The distance between the sealing plate 2and the current-collector joint 6 b 2 in the thickness direction of thesealing plate 2 is longer than the distance between the sealing plate 2and the tab joint 6 b 1. The cover portion 80 a is preferably locatednearer to the electrode body 3 than the current-collector joint 6 b 2 inthe thickness direction of the sealing plate 2. This enables thesecondary battery to have an increased volume energy density and enablesthe secondary battery to be readily manufactured. The positive-electrodeterminal 7 includes a flange 7 a, an insertion portion 7 b, and acrimped portion 7 c. The inner insulating member 11 has an insulatingmember recessed portion 11 x.

At least one support portion 80 d that projects from the cover portion80 a toward the first positive-electrode current collector 6 a isdisposed on the cover portion 80 a. The support portion 80 d ispreferably disposed between the pair of the cover joints 80 b. Aplurality of the support portions 80 d may be disposed on the coverportion 80 a. An end of each support portion 80 d is preferably incontact with the first positive-electrode current collector 6 a.Alternatively, a small gap may be formed between the end of the supportportion 80 d and the first positive-electrode current collector 6 a. Forexample, the size of the gap between the end of each support portion 80d and the first positive-electrode current collector 6 a (the distancebetween the end of the support portion 80 d and the firstpositive-electrode current collector 6 a in the thickness direction ofthe sealing plate 2) is preferably 3 mm or less, more preferably 1 mm orless, further preferably 0.5 mm or less. The end of each support portion80 d can come into contact with the first positive-electrode currentcollector 6 a when the cover portion 80 a bends. The support portion 80d enables the cover 80 to be inhibited from being damaged.

A wall portion that extends in the longitudinal direction of the sealingplate 2, a wall portion that extends in the transverse direction of thesealing plate 2, or a columnar portion can be disposed on the coverportion 80 a and used as the support portion 80 d.

The surface of the cover portion 80 a facing the electrode body 3 in thethickness direction of the sealing plate 2 is preferably nearer to theelectrode body 3 than the portion of the first positive-electrodecurrent collector 6 a and the portion of the second positive-electrodecurrent collector 6 b that are nearest to the electrode body 3. Thiscauses the electrode body 3 to come into contact with the cover portion80 a first even when the electrode body 3 moves toward the sealing plate2, and accordingly, the electrode body 3 can be inhibited from cominginto contact with the first positive-electrode current collector 6 a andthe second positive-electrode current collector 6 b.

The first positive-electrode current collector 6 a preferably includesthe current-collector projection 6 x on the surface facing the electrodebody 3. The end portion of the current-collector projection 6 x facingthe electrode body 3 is preferably located nearer to the electrode body3 than the end portion of the positive-electrode terminal 7 facing theelectrode body 3, and the current-collector projection 6 x preferablyfaces the cover portion 80 a. This enables a load can be effectivelyinhibited from being applied to the joint between the positive-electrodeterminal 7 and the first positive-electrode current collector 6 a evenwhen the electrode body 3 comes into contact with the cover portion 80a.

It is only necessary for the cover 80 to be disposed near the firstpositive-electrode current collector 6 a, or near the firstnegative-electrode current collector 8 a, or both. The cover 80 may bedisposed between the first positive-electrode current collector 6 a andthe electrode body 3, and the cover may not be disposed between thefirst negative-electrode current collector 8 a and the electrode body 3.

The inner insulating member 11 has a liquid inlet 11 f that faces theelectrolytic solution injection hole 15 that is formed in the sealingplate 2. A tubular portion 11 g that extends toward the electrode body 3is disposed around the liquid inlet 11 f. The cover portion 80 a ispreferably located nearer to the electrode body 3 than the end portionof the tubular portion 11 g facing the electrode body 3 in the thicknessdirection of the sealing plate 2. This causes the electrode body 3 tocome into contact with the surface of the cover portion 80 a facing theelectrode body 3 earlier than the tubular portion 11 g when theelectrode body 3 moves toward the sealing plate 2, and accordingly, aload can be inhibited from being applied locally to the electrode body3.

Manufacture of Electrode Body

The first positive-electrode tab group 40 a, the secondpositive-electrode tab group 40 b, the first negative-electrode tabgroup 50 a, and the second negative-electrode tab group 50 b are bentsuch that the upper surface of the first electrode body element 3 a andthe upper surface of the second electrode body element 3 b in FIG. 10are in contact with each other directly or with another memberinterposed therebetween. Consequently, the first electrode body element3 a and the second electrode body element 3 b are integrated into theelectrode body 3. The first electrode body element 3 a and the secondelectrode body element 3 b are preferably integrated with a tape.Alternatively, the first electrode body element 3 a and the secondelectrode body element 3 b are preferably integrated by being disposedin the electrode body holder 14 in the form of a box or a bag.

The outer surface of the first positive-electrode tab group 40 a that isbent preferably faces the inner surface of one of the pair of the secondwalls 11 b. The outer surface of the second positive-electrode tab group40 b that is bent preferably faces the inner surface of the other of thepair of the second walls 11 b. The outer surface of the firstnegative-electrode tab group 50 a that is bent preferably faces theinner surface of one of the pair of the third walls 13 b. The outersurface of the second negative-electrode tab group 50 b that is bentpreferably faces the inner surface of the other of the pair of the thirdwalls 13 b.

The electrode body 3 that is covered by the electrode body holder 14that is molded out of a resin sheet into a box shape or a bag shape isinserted into the prismatic exterior body 1. The sealing plate 2 and theprismatic exterior body 1 are welded to each other. The opening of theprismatic exterior body 1 is sealed by the sealing plate 2. Anelectrolyte solution is poured into the prismatic exterior body 1 viathe electrolytic solution injection hole 15 that is formed in thesealing plate 2. Subsequently, the electrolytic solution injection hole15 is sealed by the sealing member such as a blind rivet.

The electrode body holder 14 and the second walls 11 b preferablyoverlap, and the electrode body holder 14 and the third walls 13 bpreferably overlap when viewed from the direction perpendicular to theside walls of the prismatic exterior body 1 that has a larger area. Thisprevents the first positive-electrode tab group 40 a, the secondpositive-electrode tab group 40 b, the first negative-electrode tabgroup 50 a, and the second negative-electrode tab group 50 b from cominginto contact with the prismatic exterior body 1 with more certainty.

In the prismatic secondary battery 20 according to the above embodiment,the positive-electrode tab groups (the first positive-electrode tabgroup 40 a and the second positive-electrode tab group 40 b) and thenegative-electrode tab groups (the first negative-electrode tab group 50a and the second negative-electrode tab group 50 b) are disposed on theend portion of the electrode body 3 facing the sealing plate 2. Thepositive-electrode tab groups are bent and connected to the surface ofthe second positive-electrode current collector 6 b facing the electrodebody 3, and the second positive-electrode current collector 6 b isdisposed along the sealing plate 2. The negative-electrode tab groupsare bent and connected to the surface of the second negative-electrodecurrent collector 8 b facing the electrode body 3, and the secondnegative-electrode current collector 8 b is disposed along the sealingplate 2. With this structure, the secondary battery has an increasedvolume energy density.

Others

According to the above embodiment described by way of example, theelectrode body 3 is formed of the two electrode body elements. Thepresent invention, however, is not limited thereto. The electrode body 3may be formed of three or more electrode body elements. The electrodebody elements are not limited to multilayer electrode bodies and may bewound electrode bodies each of which is obtained by winding a belt-likepositive-electrode sheet and a belt-like negative-electrode sheet with abelt-like separator interposed therebetween. The electrode body 3 mayhas a single multilayer electrode body. The electrode body 3 may has asingle wound electrode body obtained by winding the belt-likepositive-electrode sheet and the belt-like negative-electrode sheet withthe belt-like separator interposed therebetween.

The cover 80 is preferably composed of a resin. For example, the cover80 is preferably composed of polypropylene (PP), polyethylene (PE), orpolyphenylene sulfide (PPS).

Examples of the energy rays used for welding include laser rays andelectron beams.

In the prismatic secondary battery 20 according to the above embodimentdescribed by way of example, the positive-electrode current collectorthat electrically connects the positive-electrode terminal and thepositive-electrode tabs to each other is formed of two components.However, the positive-electrode current collector may be a singlecomponent. In the prismatic secondary battery 20 according to the aboveembodiment described by way of example, the negative-electrode currentcollector that electrically connects the negative-electrode terminal andthe negative-electrode tabs to each other is formed of two components.However, the negative-electrode current collector may be a singlecomponent. A current interrupt mechanism may be disposed on a conductivepath between the positive-electrode terminal and the positive-electrodesheets or on the conductive path between the negative-electrode terminaland the negative-electrode sheets.

The materials of the positive-electrode sheets, the negative-electrodesheets, the separators, the electrolyte, and other components can beknown materials. According to the present invention, a battery system ofthe secondary battery is not limited. For example, the secondary batterycan be a non-aqueous electrolyte secondary battery such as a lithium-ionbattery. According to the present invention, the shape of the secondarybattery is not limited to a specific shape.

While detailed embodiments have been used to illustrate the presentinvention, to those skilled in the art, however, it will be apparentfrom the foregoing disclosure that various changes and modifications canbe made therein without departing from the spirit and scope of theinvention. Furthermore, the foregoing description of the embodimentsaccording to the present invention is provided for illustration only,and is not intended to limit the invention.

What is claimed is:
 1. A secondary battery comprising: an electrode bodythat includes a positive-electrode sheet and a negative-electrode sheet;an exterior body that has an opening and that accommodates the electrodebody; a sealing plate that seals the opening; a terminal that is securedto the sealing plate; a tab that is connected to the positive-electrodesheet or the negative-electrode sheet; and a first current collector anda second current collector that electrically connect the terminal andthe tab to each other, wherein the first current collector is connectedto the terminal, wherein the second current collector is connected tothe tab, wherein the second current collector has an opening, andwherein the second current collector is disposed on the first currentcollector and welded to the first current collector around the opening,wherein the second current collector includes a tab joint that isconnected to the tab and a current-collector joint that is connected tothe first current collector, and wherein a distance between the sealingplate and the tab joint in a thickness direction of the sealing plate isshorter than a distance between the sealing plate and thecurrent-collector joint.
 2. The secondary battery according to claim 1,wherein the tab is connected to a surface of the second currentcollector facing the electrode body.
 3. The secondary battery accordingto claim 1, wherein the second current collector includes a thinportion, and the thin portion has the opening, and wherein a portion ofthe second current collector that is located away from the opening iswelded to the first current collector.
 4. The secondary batteryaccording to claim 1, wherein an insulating member is disposed betweenthe sealing plate and the first current collector, and wherein a portionof the insulating member that faces a back surface of a portion of thefirst current collector that is welded to the second current collectorhas a recessed portion.
 5. The secondary battery according to claim 1,wherein a portion of the first current collector that faces the openinghas a flat surface.
 6. The secondary battery according to claim 1,wherein the first current collector includes a projection that has anasymmetric shape in a plan view in a region in which the first currentcollector does not face the second current collector.
 7. A secondarybattery comprising: an electrode body that includes a positive-electrodesheet and a negative-electrode sheet; an exterior body that has anopening and that accommodates the electrode body; a sealing plate thatseals the opening; a terminal that is secured to the sealing plate; atab that is connected to the positive-electrode sheet or thenegative-electrode sheet; and a first current collector and a secondcurrent collector that electrically connect the terminal and the tab toeach other, wherein the first current collector is connected to theterminal, wherein the second current collector is connected to the tab,wherein the second current collector has an opening, and wherein thesecond current collector is disposed on the first current collector andwelded to the first current collector around the opening, wherein theelectrode body includes a first tab group that includes a plurality ofthe tabs and a second tab group that includes a plurality of the tabs,wherein the first tab group and the second tab group bend in differentdirections, and wherein the first tab group and the second tab group areconnected to a surface of the second current collector facing theelectrode body.